This invention relates to automated drilling of coordination holes in parts for later assembly in a configuration determined by the location of the coordination holes, and more particularly to a method and apparatus for drilling coordination holes in stringers and stringer clips used in fabrication of transport airplanes.
A recent development in fabrication and assembly of commercial airplanes is the concept of "virtual tooling" in which the positions of parts and even the shape of the final assembly is determined by the shape and locations of parts relative to each other, and those positions are determined exclusively by the use of coordination holes drilled precisely in the parts at locations specified in the original engineering parts definitions. The set-up of the machines used to drill the coordination holes in the parts is done automatically using digital inputs from the original engineering parts definitions as the sole authority, so the possibility of error caused by misadjustment or manufacturing errors in hard tooling, as was experienced in the past, is eliminated. These hard tooling jigs and fixtures were always subject to errors during initial fabrication which, because of the complexity of the tooling design, might escape detection and produce defective parts from the beginning, or were subject to damage by rough use in the factory.
A breakthrough was made in the "virtual tooling" technology in a system disclosed in the following patent applications:
______________________________________ Appln S/N Title Filed Patent No. ______________________________________ 07/682,622 Stringer Clip End April 8, 1991 5,127,139 Effector 07/871,321 Reconfigurable Holding April 20, 1992 5,249,785 Fixture 07/964,533 Panel and Fuselage Oct. 13, 1992 Assembly 07/996,806 Workpiece Positioning & Dec. 23, 1992 5,299,894 Drilling End Effector 08/002,364 Part Positioning and Jan 6, 1993 Drilling End Effector ______________________________________
The system disclosed in these applications and patents uses a central robot which routes the edges of the panel held on a configurable fixture, and uses several different end effector to pick up parts from a parts presentation station and hold them in position against the panel while coordination holes are drilled through the part and the panel. The results obtained from use of this system has exceeded expectations in terms of consistent accuracy, but the capacity of the system is limited and adding additional systems to increase capacity was disfavored because of the cost of the central robot. Moreover, the amount of load that the robot can accurately carry and position in space places physical restrictions into the design considerations for the end effectors, resulting in use of light duty mechanisms that requires rigerous maintenance to ensure their accurate operation. However, despite and because of these problems, sufficient confidence in the virtual tooling concept was developed from experience with the original system that it was decided that the an expansion of the system would be warrented. The expansion concept is to remove the function of pads drilling from the panel cell and perform that function on machines dedicated solely to that purpose, thereby fleeing the robot from the time-consuming tasks of picking up pads and holding them against the panel while coordination holes were drilled, and changing end effectors needed for different tasks. The same original engineering parts definition will be used to program the machine controller of the machine that drills the coordination holes in the parts. If the machine is designed with sufficient accuracy and set-up checks, the coordination holes in the panel and the parts will line up perfectly when the part is at the correct position on the panel, resulting in a fabricated part that is within specifications and requires no shims. Dedicated machines designed in accordance with this expansion of the concept can be Much less costly to build and operate that the panel cell, and they can be designed to require little maintence and with even greater precision than was possible in the panel cell. Freed from the time consuming tasks required for drilling the parts, the panel cell would now be able to concentrate on routing the panel edges and drilling the coordination holes in the panel, thereby increasing the panel cell throughput.